The invention relates to a cue signal recording apparatus for a tape recorder which is adapted to use a cue signal for dictation and transcription, for example.
In a tape recorder for dictation and transcription, for example, a cue signal is used for searching for a desired recording portion while performing a fast forward (FF) or a rewind (REW) operation.
The cue signal is a sine wave signal having an extremely low frequency within a range from a few Hz to several tens of Hz and having a relatively low level. In a normal tape transport, it can not be heard as a reproduction signal. When a tape is transported for making a cue, the cue signal is acoustically reproduced. A cue signal of 30 Hz is assumed to be recorded on a tape over a 10-second distance. When such a tape is reproduced at a speed of 20 times the constant recording or normal playback speed, the cue signal is reproduced for 0.5 second with the frequency of 600 Hz. The desired recording portion may be found by detecting the cue signal of 600 Hz.
In a conventional cue signal recording apparatus, the recording of the cue signal is normally performed simultaneously with the recording of a sound for dictation. When using such conventional type of apparatus, it is difficult to record the cue signal on the same track of a recorded tape in superposing manner. The reason for this is that a bias magnetic field demagnetizes a sound signal already recorded when the cue signal is recorded. In other words, when the cue signal is superposed on the voice sound in the recording, the sound level of the recorded voice sound is extremely reduced. However, when a large amplitude cue signal is recorded with no bias, the demagnetization due to the bias magnetic field does not occur, although much of the high harmonic distortion included in the cue signal is reproduced in the constant speed transport. As described above, in the conventional device, it is very difficult to record the cue signal superposed on the speech or musical sound, without damaging the recorded sound.
An approach directed to overcome the above-mentioned disadvantages of the conventional apparatus is disclosed in U.S. Pat. No. 4,007,491. The system in this patent employs tracks 41, 42 and 44 exclusively used for index signals in addition to a sound track 40. In this proposal, when the cue signal is recorded on the tracks for index signals, the above-mentioned problem, i.e. the demagnetizing effect due to the bias magnetic field is avoidable in the superposing recording of the cue signal. This system, however, is not compatible with the conventional tape recorder provided with no index tracks, i.e. a tape recorder of which the recording track arrangement is standardized, e.g. a microcassette tape recorder.